Compared with a liquid crystal display (LCD), an organic light emission display (OLED) has the advantages such as quick response, light weight, flexibility, wide view angle, and so on. An active matrix OLED (AMOLED) is further advantageous by a low driving current and low power consumption, and is suitable for high resolution displaying.
For an LCD display device or an OLED display device, thin film transistors (TFT) are provided as control switches. The thin film transistors may comprise amorphous silicon TFT, poly-silicon TFT, oxide semiconductor TFT or organic TFT for driving. An amorphous silicon or organic TFT has low carrier mobility and low driving current, while the voltage required for driving a high brightness OLED is high and the devices occupy large space. A low temperature poly-silicon TFT has mobility up to 100 cm2/V·s, and its high current characteristic meets the strict requirements of an OLED; a low operation voltage and a high density driving structure can make the OLED having a long service life. Meanwhile, for the compensation circuit for improving grey scale and panel uniformity, in a same one pixel of the display device, a plurality of TFTs often are needed. With the high density layout characteristics of low temperature poly-silicon TFTs, the OLED panel with high brightness and high picture quality can be more easily achieved. Currently, almost all the AMOLEDs successfully put into the market employs the array substrate using low temperature poly-silicon TFT.